One thing that I have noticed during Level 1, is that as well as sobre being used for “about”, sometimes de is used during the lessons. I wondered if either or both of these sentences would be “correct”?
Quiero hablar de algo con usted
Quiero hablar sobre algo con usted
Are they interchangeable in this context or is there a subtly I am missing?
Gracias,
Stu
@gabycortinas may be able to confirm if they’re interchangeable in this particular context (I’d go strongly in the direction of ‘hablar de’ on this one, for what it’s worth) - but in general, it’s always worth remembering that prepositions are about the best examples of languages not mapping to each other - so ‘de’ sometimes is used where we’d use about, but sometimes where we’d use other things - it’s always like this, and the only way to deal with it that doesn’t involve going mad is to roll with it, use whichever comes to mind first, and let your brain get enough exposure to conversations to end up with patterns of usage similar to those you’ve been exposed to… 
That’s right. As Aran says your brain tends to select the pattern that has heard/ used the most when there is more than one option at hand. In this case both are correct.
Yes Stu, I would probably use more “hablar DE algo” than “hablar SOBRE algo”.There are many ways to express similar concepts such as:
Hablar A PROPOSITO de algo
COMENTARTE algo
DECIRTE algo
CHARLAR de algo
TOMAR UNA DECISION sobre algo
I would say that you can think it like this:
Hablar DE algo - talk ABOUT something
Hablar SOBRE algo - have a talk CONCERNING something specific that needs to be solved / decided.
Does it make any sense?
Saludos,
Gaby
This is absolutely perfecto Gaby, muchas gracias - and to you too Aran, as always 
Stu